Planar media magnetic code identification system



Dec. 20, 1966 D. s. OLIVER 3,293,629

PLANAR MEDIA MAGNETIC CODE IDENTIFICATION SYSTEM Original Filed April12, 1960 4 Sheets-Sheet 1 INVENTOR. 00mm 5. OLIVER Dec. 20, 1966 D. s.OLIVER 3,293,629

PLANAR MEDIA MAGNETIC CODE IDENTIFICATION SYSTEM 4 Sheets-Sheet 2Original Filed April 12. 1960 6 FIG. 7

INVENTOR. DONALD S OLIVER D. s. OLIVER 3,293,629

PLANAR MEDIA MAGNETIC CODE IDENTIFICATION SYSTEM Dec. 20, 1966 4Sheets-Sheet 3 Original Filed April 12, 1960 a w a/ q 5 N X M a V f\ 8 Mw m H H H Xm m M s i) N a a H on I FLUX LIN KING READING EN) COI I.

POSITION VOLTAGE TIME NDUCED IN HEAD COIL I XIA XZA XSA X4A XSAINVENTOR. DONALD S. OLIVER Dec. 20, 1966 D. s. OLIVER 3,293,629

PLANAR MEDIA MAGNETIC CODE IDENTIFICATION SYSTEM Original Filed April12. 1960 4 Sheets-Sheet 4 q VOLTAGE mouceo m READING new MILLIVOLTSconveunomu LONGITUDINAL kecolwmo (A 14 MILS) TRANSVERSE RECORDING NORMALO lllllllll! ||||z .om .005 .ono .ons .020

HEAD MEDIUM SEPARATION (inches) FIG. 9

IN V EN TOR.

DONALD S. OLIVER BY scanned digital code.

United States Patent f 3,293,629 PLANAR MEDIA MAGNETIC CODEIDENTIFICATION SYSTEM Donald S. Oliver, West Acton, Mass., assignor toItek Corporation, Lexington, Mass., a corporation of DelawareContinuation of application Ser. No. 21,754, Apr. 12, 1960. Thisapplication Apr. 2, 1965, Ser. No. 449,358

5 Claims. (Cl. 340-1741) This is a continuation of US. application21,754 filed April 12, 1960, now abandoned.

This invention relates to a method and means for magnetic recording andreading; it particularly concerns (1) means for transversely recordingon a magnetic stripe in a manner permitting the recorded information tobe read from the edge of the stripe and (2) a method of sensing magneticdata which has been prerecorded transversely, as aforesaid.

The science of data storage and retrieval in a magnetic medium is welladvanced and a variety of different embodiments have been devisedtherefor. Most familiar of the techniques is that of recording datasignals and reading on magnetic wire or magnetic tape arranged as acontinuous ribbon of material which is advanced from one reel toanother. In this way, by putting a stripe of magnetic material oncinemaphotographic film, it is possible to correlate a sound trackrecorded on the stripe with motion of the image frames.

Data storage on film is, of course, well known; microfilming of graphicinformation is now conventional. In its usual embodiment, information isreduced 30-50 times and arranged in an array of discrete frames on thecontinuous film ribbonand wound on a reel. Location of a particularframe on the reel in the simplest applications is performed by manualoperations and visual observation until the desired data is brought intoview. A more sophisticated technique employs a reel of film having amagnetic stripe along one edge. This stripe has data recorded thereonidentifying the adjacent or a nearby image frame. An associatedmechanism may be connected to the magnetic transducer sensing theidentification data to stop the reels and present a preselected frame tothe viewer on a projection screen.

Because of the obvious inconvenience of storing on reels data which issubject to random retrieval, various attempts have been made to divideup the image frames into film segments or film chips which can be storedin a compact array. In one system individual microfilm segments aresecured to or made part of a punched card and are handled by familiarpunched card sorting techniques. In another current system,identification data is put on the film surface in the form of anoptically A major disadvantage of such a system is that it requires thatat least part of the surface of each chip be made accessible duringidentification scanning. This is time consuming, definitely increasingthe time required to search a given store and probably most important,increases mechanical complexity while simultaneously exposing thesurfaces to abrasion and thereby hastening deterioration. Precisely thesame drawbacks would exist if the film had an identification magneticstripe coded in the conventional manner; as with an optically sensedcoded surface, conventional recording on .a magnetic stripe wouldrequire access to the surface of the stripe.

A simple analogy may be made by a comparison with the technique ofsearching for a particular book title out of a multitude of booksarranged in the usual manner on shelves. Assuming the books had noidentification on the spines, if each book had to be removed, evenpartially, from the shelf in order to observe the title on 3,293,629Patented Dec. 20, 1966 the front cover, the rapidity of such a searchwould be extremely limited; retrieval time for a particular title wouldbe excessive. It is obviously far more convenient and considerablyfaster to scan the title or identification numbers from the spinesurfaces which are exposed adjacently on the shelves. In a comparablemanner, scanning a multitude of discrete, information bearing sheetssuch as film chips, which are stacked in a closely packed array byreading an identification code off the chip edges might become thesolution for rapid search and immediate access to a predetermined chip.But conventional magnetic recording and reading techniques do not permitthe certain and unambiguous sensing of magnetic information from theedge of a magnetic stripe.

It is an important object of this invention accordingly, to provideapparatus for recording an identification code in a magnetic medium,such as the striping on a film chip, which may be sensed by transducermeans positioned beyond the outer edge of the stripe. Another importantobject of this invention is to provide a method for sensing magneticdata from the outer edge of the stripe.

Basically, the invention comprises magnetization of a magnetic stripe ina direction transverse thereto and sensing the fringing flux whichexists (under the proper circumstances) at the outer edge of the stripe.Transverse is here defined as the dimension across the width of a mediumwhich is termed longitudinal along the length of the stripe, itsthickness being much less than its width. The process may utilize, forexample, an information bearing sheet such as a film chip having astripe of magnetizable material on one surface at an edge thereof. Aspecial magnetic recording means is brought into juxtaposition with themagnetic stripe and aptly positioned to cause transverse magnetizationin a binary coded pattern of bits having a code arranged in a pluralityof unique N and S orientations. The edge of the film chip carrying themagnetic stripe is caused to have relative motion with a stackedtransducer unit having a sensing or reading head for each code bit. Thefringing flux which exists beyond the outer stripe edge links the gap ofeach head and may thus be detected. It should be noted that thepossibility of reliably sensing the encoded bits from the outer edge ofa magnetic stripe turns upon achieving a substantial fringing flux,i.e., a transversely magnetic recorded code bit must have a significantflux external the stripe edge to properly coact with an appropriatetransducer pick-up or reading head.

Transverse recording is accomplished in the present invention by havinga recording head with an unconventionally long gap between the polefaces, the length of which is approximately equal to or greater than thewidth of the magnetic stripe. Placed within the gap of the recordinghead is an electrically conductive nonmagnetic material. When thisrecording transducer is properly energized, eddy currents in thematerial within the gap causes the magnetization flux to be detouredoutside the gap but substantially parallel to its length. The accessibleouter surface of the material filling the gap of the recordingtransducer is placed in contacting, transverse relationship with themagnetizable stripe. Since the flux is forced to detour outside the gapit causes a remanent, transverse magnetized pattern to be formed in thestripe which has a substantial field beyond the external edge of thestripe.

An alternative technique for surface recording magnetic information andsensing from the edges of the medium might be recording perpendicular tothe medium, i.e., through the thickness of the material. In a sense,this would be the obvious technique but on closer examination certaindrawbacks come into focus. If the medium is a conventional magneticcoating of 1 mil thickness the length of the magnetic bit formed in themedium is also about 1 mil. Since the track width of recordingtransducers is generally -50 mils, the aspect ratio in perpendicularrecording, that is, the ratio of magnet length (L) to the pole face area(A) is not good; because of the small L, the effect ofself-demagnetization is appreciable. To increase the aspect ratiorequires decreasing the width of the recording transducer gap therebydecreasing the flux available. With a medium 25 mils wide, and 1 milthick, and a 40 mil gap width, defining aspect ratio for comparisonpurposes as L/ /A, where L=1 A :25 X 40 therefore L 1 VTWTFO Transverserecording produces an aspect ratio L/ /A wherein the length (L) of themagnet is the width of the stripe which will be, perhaps, 25 mils. Usinga 40 mil recording track yields an aspect ratio of 25/ /40, 125 timesbetter than that achieved with prependicular recording.

There is still another disadvantage of perpendicular recording; spacingloss is increased. Spacing loss is the fall off of induced voltage in areading head as it is moved away from the recorded medium. As thedistance between the magnetized bit and the transducer gap becomeslarger, the relative distances from the gap to each of the two poles ofthe bit becomes proportionately smallerfurther causing a cancellation ofthe field of each pole at the reading head.

An unexpected advantage results from the technique of transverserecording and edge sensing. In the general equation for the voltageinduced in the reading head (it ,u-I-l the term etells how thereproduced voltage depends on spacing. In order to compare this computedeffect with the experimentally observed one it is necessary to put it indecibel form by computing twenty times the log of e giving: Spacingloss=54.6 (d/A) in decibels; where d spacing between a head andrecording medium and )\=recorded wavelength.

It was discovered that as the sensing transducer employed in thisinvention was increasingly spaced away from the magnetically coded edgesthe rate of signal decrease was significantly less than what waspredicted from experience with conventional recording and readingtechniques. The experimental data and interpretation of resulting curvesis elaborated more fully in the detailed description following.

Other objects and features of the invention will become more apparent asthe description proceeds in which:

FIG. 1 is a perspective View of a data bearing sheet such as a filmchip, having a stripe of magnetic material on a surface near an edge,the stripe as shown being somewhat exaggerated in thickness;

FIG. 2 is a plan view of a number of film chips having relative motionwith respect to a magnetic transducer reading unit which is positionedadjacent the chip edges having the magnetic striping;

FIG. 3 is a detail view of an individual chip showing a single channeltransducer head adjacent to a single recorded bit;

FIG. 4 is a perspective view of a recording transducer in operativeposition, and appropriate recording circuitry shown schematically;

FIG. 4A is a detail of the recording transducer shown in FIG. 4;

FIG. 5A is a diagrammatic illustration of a film chip with a binarycoded edge;

FIG. 5B is perspective view of the film chip illustrated in FIG. 5A, themagnetic fields of some of the bits shown in their conventionalrepresentation;

FIGS. 6 and 7 show alternative transverse recording means;

FIG. 8A shows diagrammatically the spatial relationships involved in theedge sensing technique;

FIGS. 83 and 8C are corresponding waveforms for phenomena resulting fromthe interrelationships shown in FIG. 8A;

FIG. 9 is a diagram indicating relationship of induced voltage withtransducer spacing comparing conventional and transverse recording.

One form of data-bearing sheet which embodies the principles of thisinvention can be seen in FIG. 1. This particular data sheet 20, called afilm chip, is a length of 16 mm. film suitable for use in microfilmingwhich has a thin, narrow stripe 21 of magnetic material on the basesurface 22 at one edge 23. Means which form no part of this inventionare provided at 24 for permitting a plurality of physically similar filmchips 20 to be arranged in a densely stacked storage array, such as amagazine (not shown), and to slide or hinge one by one past a magnetictransducer reading head 25 as shown in FIG. 2.

Using conventional identification techniques, the searching of a stackof film chips 20 would require access to the surface 22 of each chip.For example, referring to FIG. 2, a plurality of film chips 22 can beseen in diagrammatic representation. If the chips 20 were comparable tobooks arranged on a library shelf, techniques which employ an opticallysensed identity code or a conventional face sensed magnetic code on thefilm surface 22, would require sequentially displacing each chip fromthe stack and causing each coded surface to be displaced for sensinguntil the desired chip was located. As shown in FIG. 2, if a magneticfield exists at the edges of the chips 20, a magnetic transducer readinghead or pickup 25 having relative motion in respect to the coded edges23 can rapidly scan all of the chips 20 in the stack or magazine withoutdisturbing or displacing any of the chips.

As clearly indicated in FIG. 1 by the arrow 30, the desiredmagnetization must be in a direction transverse to the magnetic stripe21. One arrangement generally designated at 31 for accomplishingtransverse magnetization can be seen in FIG. 4. A magnetic core 32 has agap 33 with a length 34 substantially equal to the Width 35 of themagnetic stripe 21, the core being positioned with that gap transverselyacross the stripe. The gap 33 has an insert 36 between the pole faces 37and 38 made of a material which is non-magnetic and possesses goodelectrical conducting properties, for example, copper. A number of turns39 of wire are coiled around the core 32 and connected through oneterminal 41 of a twoposition switch 42 to a large capacitor 43. Theother terminal position 44 of the switch 42 disconnects the capacitor 43from the core winding 39 and connects it to a charging source such as abattery 45. When the switch 42 is closed in the capacitor chargeposition at 44, the capacitor 43 charges in the expected manner untilthe potential thereacross equals the potential of the source 45 or untilcharging is interrupted by disconnect ing the switch. If the switch 42is now shifted to terminal 41 connecting the charged capacitor 43 to thecore winding 39, the capacitor will discharge through the winding,creating a sharp initial current pulse which then decays at aconsiderably slower rate.

The initial, steeply rising pulse of current causes a correspondingmagnetic flux in the core 32 having a direction which is determined bythe direction of current fiow in the winding 39. Without thenon-magnetic insert 36 in the gap 33 between the pole faces 37 and 38 ofthe core 32, the magnetic flux in the core would bridge the relativelyhigh reluctance air gap to complete the magnetic circuit. However, theconductive insert 36 has induced therein by the increasing magneticfield, substantial eddy currents which produce a magnetomotive force(M.M.F.) opposing the initial d/dt. This opposite within the insert B6tends to force the primary magnetic flux in the core 32 outside andaround the external margin of the gap 33 and the insert and transverselythrough the magnetic stripe 21 as shown in FIG. 4. The insert 36 has anexterior surface 50 which is substantially flush with the externalmargins 51 of the gap faces 37 and 38. The internal surface 52 of theinsert 36 extends considerably beyond the internal margin 53 of the gapfaces 37 and 38. As a result, when the core winding '39 is energized,the counter-M.M.F. induced in the insert 36 will be more effective inblocking a flux path in the interior of the core 32 than exterior to it.Accordingly, the path of least reluctance will be parallel to theexterior face 50 of the insert 36 and through the stripe 21.

The capacitor discharge pulse is initially very steep causing dq5/dt tobe high, and it then decays considerably more slowly resulting in a lowd/dt. After a brief period the recording assembly 31 may be removed fromthe stripe 21, the stripe having a remanent magnetic field creating acode bit 54 of some predetermined orientation. Of course, the directionof the field across the width 35 of the magnetic stripe 21 determinesthe orientation of the magnetic poles of the remanent magnetic field. Toreverse the polar orientation requires only that the charging current incore winding 39 be reversed. This may be accomplished by simplyconnecting leads 55 and 56 of capacitor 43 to the winding at 46 and 47respectively.

While the foregoing description is concerned with recording a singletransverse bit or sector 54, it is clear that a plurality of bits 54A,B, C, D, etc., may be recorded simultaneously to encode a single chip 20with its complete binary identification code. A chip is shown in FIGS.5A and 5B which has a plurality of bits 54 in a coded pattern.

A considerable advantage of transverse recording in the manner describedis that recording takes place while the magnetic stripe 21 is fixedrelative to the recording unit 31. This permits accurate positioning ofan imagebearing entity 20 in respect to recording transducer 31 so thatcorresponding tracks or segments 54 on each entity are at the samephysical location relative to the dimensions of all the physicallyidentical entities. The proper registration of succeeding chips 20 withrespect to the tracks on a reading head 25 is thus assured.

As explained above, each chip 20 is given a particular identificationcode of an arrangement or pattern of binary polarized magnetic bits 54on the magnetic stripe 21 (see FIGS. 5A and SB). One such bit 54Arepresented by the dotted lines in FIG. 3 is shown in operativerelationship with a single channel element or head 25A of the readingtransducer 25. As the magnetized segment 54A passes the reading headchannel 25A, a voltage is induced therein having a magnitude which is afunction, amongst other factors, of the field strength of the bitexternal the edge 23 of the stripe 21, head-medium spacing and therelative velocity between head 25A and bit 54A.

This relationship is shown in the presentation of FIGS. 8A, 8B, and 8Cwherein two adjacent film chips 20A and 20B are shown in fragmentarydetail. A single element 25A from the multitrack reading head 25 isindicated having relative motion in respect to code bit segments 54A and54B of the two chips which are located at the same physical location oneach chip. As the external field of the magnetized segment 54A on chip20A comes closer to the transducer pickup 25A, it will be noted fromFIG. 8B that the flux represented by the downward arrows in FIG. 8Aincreasingly links with the iron core 32 of the pickup to a maximumpoint; the linkages decrease more rapidly to zero when the head is justopposite the magnetic bit and proceeds to a negative maximum as the headpasses center, the flux linkage rising to zero as the head passes out ofthe external field. The voltage e induced in the reading head 25A, is aswell known, a function of the expression d/dr; the flux linkages(plotted in FIG. 8 3) between the reference points x and x yield thesignal pulse 60 illustrated in FIG. 8C.

An identical sequence will occur for the adjacent film chip 2013, theonly difference being the reversed polarity of the correspondingmagnetic bit 5 4B. This difference yields an identical butopposite-going pulse 61 from that derived from the corresponding bit 54Aof the previous chip 20A.

In the usual circumstances, the unique identity code for a particularfilm chip 20 will consist of a number of variously polarized transversesegments 54 making up a unique pattern of magnetic bits; such a patternis diagrammatically indicated by FIG. 5A, and the orientation of themagnetic fields making up the code pattern can be seen in thehypothetical representation of FIG. 5B. A standard, commerciallyavailable transducer 25 having the individual sensing elements 25A, 3,C, D, etc., may thus be positioned in operative relationship withrespect to the magnetized segments on the magnetic stripe 21corresponding to each sensing element of the transducer pickup. Relativemotion of each chip 20 in respect to the stacked multi-element,transducer 25 produces a pattern of electrical pulses corresponding toan identity code comprising the pattern of magnetic bits 54A, B, C, D,etc., on the edge 23 of each succeeding film chip.

Having now described the invention in terms of its general aspects andembodiments, it is now useful to turn to specific illustrations of itsoperation. A representative information-bearing sheet 20 which cansuccessfully exploit the possibilities inherent in edge sensing oftransversely recorded magnetic data is a film chip. A typical film chip20 will be formed from a 2% inch length of 16 mm. film having a ferricoxide stripe 21 at one long edge 23 thereof. Such a film chip 20 may besevered from standard, commercially available film stock which has amagnetic stripe 21 designed for a sound track application. Thedimensions of the stripe are 0.025" in width by about .001" thick.

vBecause a standard, commercially available reading head 25 is providedwith fourteen channels per inch, each channel being .040" wide withapproximately the same spacing between channels, it is feasible torecord and read a 28 bit code on a chip 2%" long. Recording heads 31with multiple elements 31A, B, C, D, etc., can be positioned in respectto the edges 23 of each chip 20 as previously described and the codedidentity designation put on the magnetic stripes 21 as different uniquepatterns of polarized magnetic bits 54. The width 62 of each magneticsegment 54 or track recorded, and the space 63 between adjacent segmentsare a function of the specifications of the standard twenty-eightchannel reading head 25. It should be emphasized, however, that theprinciple of transverse magnetization and edge sensing thereof is notdependent on conventional dimensions. Considerable success has beenshown using a bit packing density of double that described, viz.,recording a .020" track with a spacing of .040 between adjacent tracks.Moreover, careful recording techniques to reduce the flux fringing theprimary field will permit closer spacing of adjacent tracks to furtherincrease the number of tracks per unit distance along the magneticstripe 23.

In a typical recording circuit of the type illustrated in FIG. 4, therecording circuit for each track or bit 54 is formed on a stripe of.025" width. A DC. voltage source 45 which can be a battery of 10-15volts is connected selectively in either polarity to capacitor 43. Toavoid ringing, a large capacitor 4:3, for example a ,ufd.

electrolytic, is employed. The RC time constant of the charging circuitfor capacitor 43 is relatively short. The discharge circuit is throughthe core winding 39 Where L:300 mh. at 1 kc. and 12:54 ohms. The L/Rratio is kept low to produce the desired fast rise time for a high d/dt.

Clearly, the technique for achieving transverse polarization of codesectors 54 along the stripe 21 is not limited to the particular form ofapparatus described above, a so-called in-gap technique is alsoavailable. In the slotted toroid 74 of FIG. 6, an auxiliary Winding 71is Wound through holes 72 punched in the annular core 73 on either sideof a radial notch 74 in the external margin of the core. Themagnetomotive force developed by this Winding 71 saturates the materialof core 73 in the area around these holes 72 thus diverting the fluxproduced by a main Winding 75 through the magnetic striping 21 in thenotch 74 in a transverse direction.

In FIG. 7, the geometry of a core 80 is such that the core material issaturated in the area 81 of the magnetic 20 stripe 21 so that most ofthe magnetomotive force produced by the coil 82 is impressed across theWidth 35 of the stripe, thereby magnetizing it in a transversedirection.

It is evident that still other variations will occur to those skilled inthis art and it is not intended therefore to confine the invention tothe precise embodiment described here, but rather to be governed by thespirit of the invention as defined within the ambit of the claims,accordingly I claim:

1. A data bearing media identification system comprismg:

(a) planar media having data recorded on the planar faces of said media,

(b) a magnetizable region afiixed only to planar faces of said mediaadjacent edges of said media and magnetized to produce remnant fluxemanating from said edges in a direction substantially perpendicular to0 said edges in accordance with an identity code indicative of said datarecorded, and

(c) means for determining the identity of said media, saididentification means including means for sensing the remnant fluxemanating from said edges.

2. A data bearing media identification system as set forth in claim 1wherein the magnetic poles formed in said magnetizable region arepositioned substantially along a line normal to the planes of the edgeof said media.

3. A data bearing media identification system as set forth in claim 1wherein said magnetizable region is a strip secured to said planarfaces.

4. A data bearing media identification system as set forth in claim 3wherein the magnetic poles formed in said magnetizable region arepositioned substantially along a line normal to the planes of the edgesof said media.

5. A method of identifying a plurality of planar data bearing mediacomprising the steps of:

(a) recording data in planes substantially parallel with the planes ofsaid media,

(b) recording remnant magnetic flux in accordance with an identity codeindicative of said data recorded within strata of magnetiza-ble materiallying in planes substantially parallel with the planes of said media andpositioned adjacent the edges of said media and, (c) sensing the remnantmagnetic flux emanating substantially perpendicular to the edges of eachof said data bearing media to identify said media.

References Cited by the Examiner UNITED STATES PATENTS 2,857,059 10/1958Goerlich et a1 340-174.1 3,034,643 5/1962 Keller et al 340174.1

BERNARD KONICK, Primary Examiner.

A. I. NEUSTADT, Assistant Examiner.

1. A DATA BEARING MEDIA IDENTIFICATION SYSTEM COMPRISING: (A) PLANARMEDIA HAVING DATA RECORDED ON THE PLANAR FACES OF SAID MEDIA, (B) AMAGNETIZABLE REGION AFFIXED ONLY TO PLANAR FACES OF SAID MEDIA ADJACENTEDGES OF SAID MEDIA AND MAGNETIZED TO PRODUCE REMNANT FLUX EMANATINGFROM SAID EDGES IN A DIRECTION SUBSTANTIALLY PERPENDICULAR TO SAID EDGESIN ACCORDANCE WITH AN IDENTITY CODE INDICIATIVE TO SAID DATE RECORDED,AND (C) MENS FOR DETERMINING THE IDENTITY OF SAID MEDIA, SAIDIDENTIFICATION MEANS INCLUDING MEANS FOR SENSING THE REMNANT FLUXEMANATING FROM SAID EDGES.